This invention relates to detecting the occurrence and specific location of leaks and checking hydrogen removing cells in absorption chillers.
Absorption chillers have found great favor because they are quite compatible with the environment, and do not use electricity to drive the cooling process, but rather utilize heat which may, in many instances, be waste heat from other processes, which further favors the environment. Absorption chillers are utilized in various sizes, but typically are quite large, ranging from three to five meters in diameter and eight to fifteen meters in length, for instance. Because of this, and because of the fact that the operating pressure of an absorption chiller is less than about six torr, there is a great opportunity for leakage to occur. Atmospheric air (about 760 torr) will enter the chiller through the leaks. The absorption chillers utilize lithium bromide in solution with water. In one phase of the process, the lithium bromide is very concentrated and hot, and extremely corrosive. When air enters through leaks, the oxygen in the air supports the corrosion of the metal parts. Further, the large fraction of nitrogen in the air impedes the absorption of water vapor into the lithium bromide solution, thereby significantly reducing the effectiveness of the chiller process.
When air enters the chiller and accelerates corrosion of the metal parts, metal ions dissolving into the aqueous /LiBr solution release hydrogen, and the H2 impedes the absorption of water vapor by the lithium bromide solutions, thereby denigrating chiller performance. It is therefore conventional to utilize hot palladium cells to extricate the hydrogen. However, there is no way to determine from outside the chiller whether the palladium cells are working, or not.
In the prior art, the occurrence of a leak is usually detected by observation of severely reduced chiller performance. This becomes a major event in large buildings, particularly hospitals, when the building environment can no longer be controlled because of chiller shut-down, due to the leaks. Thereafter, determining the location of the leak is a separate and lengthy process. One method which has been used in the past is to spray Freon all over the outside of the chiller, one area at a time, so that Freon will enter the chiller when sprayed near the leak, and the presence of Freon within the chiller is sensed by a Freon sensor attached through the wall of the chiller. However, this process is not very effective. Another process used in the prior art is to pressurize the interior of the chiller with Freon to more than atmospheric pressure, and utilize portable Freon detectors, moved all over the exterior surfaces, to sense where Freon exits the chiller, thereby identifying the location of the leak. This process requires that the chiller be shut down for three or four days, which is excessive.
In this process the chiller is filled with pure nitrogen instead of air because the oxygen in air would increase the rapid oxidation (corrosion) of the internal metal surfaces. Most of the lithium bromide and water vapor are removed first. Then a nitrogen mixture with a small amount of ordinary refrigerant (such as 134A, for instance) is utilized to pressurize the chiller above atmospheric pressure. A refrigerant detector is utilized, being moved over the entire external surface of the chiller, to locate the leak. Subsequently, the nitrogen/refrigerant mixture has to be pumped out of the chiller, completely, since the presence of even traces of nitrogen or other extraneous gas, even at only a few millitorr pressure will denigrate chiller performance.
With the Freon detection process, the sensitivity of the leak detection process is set by the detector""s ability to detect Freon. Since chloro-Freons can no longer be dumped into the atmosphere, only fluoro-Freons like 134A can now be used. These Freons cannot be detected at the low concentrations with low-cost sensors where chloro-Freon could be detected using relatively low-cost sensors. Expensive sensors using mass spectrometry principles operate at low pressure but cannot operate in the presence of water vapor. Furthermore, greater leak sensitivity can be achieve by using low molecular weight molecules because the rate at which a molecule diffuses through a leak varies with the square root of the molecular weight. Therefore, under similar conditions, helium (He) will diffuse through a leak about five times faster than a Freon like 134A.
Objects of the present invention include an on-line absorption chiller leak detector that operates continuously, without human intervention; an absorption chiller leak detector that can detect leaks prior to significant deterioration of chiller operation, thereby permitting corrective action to be taken without the chiller having failed or being required to be shut down; absorption chiller leak location which can be performed while the chiller is operating; absorption chiller leak location which does not require shutting down the chiller; absorption chiller leak location which does not require insertion and/or removal of substances which are incompatible with chiller operation; absorption chiller leak location which is extremely inexpensive and very effective; absorption chiller leak location which is very fast, not requiring multiple days; absorption chiller leak detection and location which promotes continuous operation of the chiller during the detection and location processes; and checking hydrogen removing cells in an absorption chiller.
According to the present invention, an on-line, un-manned absorption chiller leak detector comprises a low-cost hydrogen sensor, such as a palladium-silver solid state sensor or a palladium micro-cantilever (known as a Micro Electrical Mechanical System, or MEMS), with accommodation for water vapor. In one form of the invention, the sensitivity of the hydrogen detector to water vapor is compensated for in the signal processing; in another form of the invention, water vapor is prevented from reaching the sensor by virtue of a membrane that passes light gases and blocks the transmission of water vapor.
In accordance further with the invention, the location of leaks in an absorption chiller is achieved by spraying helium at all necessary specific locations on the exterior of the chiller, and sensing the movement of helium into and through the interior of the chiller by means of a conventional helium leak detector which is modified by blocking water vapor therefrom, the water vapor being blocked by either or both of a membrane that will pass the light gases but not water vapor, and/or a water vapor trap (such as a condenser).
The present invention provides a means for early detection of chiller leaks, without human intervention. The invention permits leak location without shutting down the chiller, without emptying it and repressurizing it with a leak detection gas, and without purging the leak detection gas. The present invention permits sensing leaks which are much smaller than the leaks that were capable of being detected by the use of Freon sprays, such as ten to 1000 times smaller leaks. Furthermore, the present invention, utilizing helium as the detectable entry substance, is very fast, sensing the presence of induced helium within seven to ten seconds, in most cases, making it relatively easy to retrospectively locate the leak precisely.
In further accord with the invention, hydrogen concentrations may be monitored to determine the efficacy of hydrogen-removing, hot palladium cells.
Other objects, features and advantages of the present invention will become more apparent in the light of the following detailed description of exemplary embodiments thereof, as illustrated in the accompanying drawing.